THS4271_16 Datasheet, PDF (24/50 Pages) Texas Instruments – LOW NOISE, HIGH SLEW RATE, UNITY GAIN STABLE VOLTAGE FEEDBACK AMPLIFIER

THS4271
THS4275
SLOS397F – JULY 2002 – REVISED OCTOBER 2009
50 Ω
Source
V_I
49.9 Ω ^RT
+5 V
+
THS4271
_
R_ISO ^{0.1 µF}
16.5 Ω
68 pf
-5 V
R_f
249 Ω
R_g 249 Ω
1.82 kΩ
IN
ADS807
12-Bit,
CM 53 Msps
IN
0.1 µF
For best performance, high-speed ADCs should be driven
differentially. See the THS4500 family of devices for more
information.
Figure 79. Driving an ADC With a
Single-Ended Input
Using the THS4271 as a DAC Output Buffer
Two example circuits are presented here showing the
THS4271 buffering the output of a digital-to-analog
converter. The first circuit performs a differential to
single-ended conversion with the THS4271
configured as a difference amplifier. The difference
amplifier can double as the termination mechanism
for the DAC outputs as well.
3.3 V 3.3 V
100 Ω
100 Ω
DAC5675
14-Bit,
400 MSps
249 Ω
124 Ω
249 Ω
249 Ω
+5 V
_
THS4271
+
-5 V
249 Ω
49.9 Ω
RF
LO
Figure 80. Differential to Single-Ended
Conversion of a High-Speed DAC Output
For cases where a differential signaling path is
desirable, a pair of THS4271 amplifiers can be used
as output buffers. The circuit depicts differential drive
into a mixer IF inputs, coupled with additional signal
gain and filtering.
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3.3 V 3.3 V
100 Ω
100 Ω
1 nF
THS4271
+
_
C_F
DAC5675
14-Bit,
400 MSps
249 Ω
100 Ω
249 Ω
249 Ω
249 Ω
1 nF
C_F
_
1 nF
IF+
49.9 Ω
49.9 Ω
RF_(out)
IF-
1 nF
+
THS4271
Figure 81. Differential Mixer Drive Circuit
Using the DAC5675 and the THS4271
Active Filtering With the THS4271
High-frequency active filtering with the THS4271 is
achievable due to the amplifier high slew-rate, wide
bandwidth, and voltage-feedback architecture.
Several options are available for high-pass, low-pass,
bandpass, and bandstop filters of varying orders. A
simple two-pole low pass filter is presented here as
an example, with two poles at 100 MHz.
50 Ω Source
V_I
249 Ω
61.9 Ω
6.8
pF
249 Ω
5V
_
THS4271
+
−5 V
49.9 Ω
V_O
33 pF
Figure 82. A Two-Pole Active Filter With Two
Poles Between 90 MHz and 100 MHz
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